Intraoperative Flash Visual Evoked Potential Recording and Relationship to Visual Outcome

Abstract

Objective: To determine the relationship between intraoperative flash visual evoked potential (FVEP) monitoring and visual function. Methods: Intraoperative FVEPs were recorded from electrodes placed in the scalp overlying the visual cortex (Oz) after flashing red light stimulation delivered by Cadwell LED stimulating goggles in 89 patients. Restrictive filtering (typically 10-100 Hz), optimal reject window settings, mastoid reference site, total intravenous anesthetic (TIVA), and stable retinal stimulation (ensured by concomitant electroretinogram [ERG] recording) were used to enhance FVEP reproducibility. Results: The relationship between FVEP amplitude change and visual outcome was determined from 179 eyes. One eye had a permanent intraoperative FVEP loss despite stable ERG, and this eye had new, severe postoperative visual dysfunction. Seven eyes had transient significant FVEP change (>50% amplitude decrease that recovered by the end of surgery), but only one of those had a decrease in postoperative visual acuity. FVEP changes in all eight eyes (one permanent FVEP loss plus seven transient FVEP changes) were related to surgical manipulation. In each case the surgeon was promptly informed of the FVEP deterioration and took remedial action. The other eyes did not have FVEP changes, and none of those eyes had new postoperative visual deficits. Conclusions: Our FVEP findings relate to visual outcome with a sensitivity and specificity of 1.0. New methods for rapidly acquiring reproducible FVEP waveforms allowed for timely reporting of significant FVEP change resulting in prompt surgical action. This may have accounted for the low postoperative visual deficit rate (1%) in this series.